Domestic Grey water is defined as all waste water generated from household sources other than from a flushing toilet. Toilet waste water is known as ‘black water’. In circumstances in which a homeowner/builder adopts the use of a waterless composting toilet to manage human waste, effectively eliminating the black water component of the waste stream, the remaining grey water needs to be managed in some form.
The reason we promote the separate management of grey water is to avoid wasting water on managing your toilet. Also, by keeping black water separate from grey water you avoid contaminating tens of thousands of litres of water with potentially harmful (pathogenic) bacterial. This means the grey water is much easier to treat to a sufficient standard to be dispersed above or below ground.

On average, Australian households use a total of 240,000 litres of water a year if they have a flushing toilet. According to the Victorian Plumbing Industry Commission a 5,000L rainwater tank on a 100m2 roof area would yield 60,000L per year. So as well as reducing a household’s water demand by installing a waterless toilet, reusing grey water in an effective manner is also vital to the design of a self-sufficient sustainable home.